I know plenty of adults with unexplained back problems...it could be from a number of things, but I wouldn't rule out that those carriers could have contributed.
Speaking of hip/joint development...my daughter loves to be carrier in what is essentially a front facing crotch dangling position. I'm considering getting a jumperoo. She's only 10 weeks, holding her head up and sitting assisted. I'm not sure if she's too young for it, 3 months is recommended.
Those are also cited for hip and spine problems, but if she's only in it for 10-15 mins at a time for no more than 30-45 minutes a day, it should be fine, right?
Does anyone use one, and how did you know your baby was ready for it?